Microparticles, generally, and cellulose ester and cellulose microparticles, specifically, and the processes for making each are not new. For example, see U.S. Pat. Nos. 4,090,022; 4,063,017; 4,551,389; 4,663,447; 4,024,334; 4,390,691; and 4,461,892. Each said patent shall be discussed in detail hereinafter.
U.S. Pat. Nos. 4,090,022 and 4,063,017, both to Tsao et al, are directed to cellulose beads made from a cellulose ester precursor. Tsao et al's process requires the following steps: (a) dissolving a cellulose derivative in a "inert organic, water miscible solvent", thereby forming a solution; (b) forming the solution into droplets by spraying and allowing the droplets to fall to a precipitation bath; (c) precipitating the solution in the precipitating bath which consists of water; (d) separating and washing the beads from the bath; and (e) hydrolyzing the beads to cellulose The "inert organic-water miscible solvent" used to dissolve the cellulose derivative is 100% organic solvent (slight amounts of moisture, normally existing in commercial grades of the solvent, are tolerable). Examples of the solvents are set forth in columns 5 and 6 of U.S. Pat. No. 4,090,022. The criticality of the "solvents" composition is set forth in U.S. Pat. No. 4,090,022 at column 4, lines 43-60.
U.S. Pat. Nos. 4,551,389 and 4,663,447, both assigned to Daicel Chemical Industries, Limited of Japan, are directed to porous cellulose acetate microparticles. The process by which these microparticles are made include the steps of: (a) dissolving the cellulose acetate in a solvent of acetic acid and water and thereby forming a dope; (b) forming the microparticles by injecting the dope through a nozzle directly into the coagulation bath where an agitator blade cuts the dope into small particles; (c) coagulating the cut dope in the coagulation bath which consists of water and acetic acid; and (d) separating and washing the microparticles. The solvent for the dope consists of a mixture of acetic acid and water in ratios ranging from 80/20 to 90/10. The coagulation bath consists of a mixture of water and acetic acid in ratios ranging from 70/30 to 58/42. These process steps are critical to the formation of the beads because those steps allow the formation of a tough shell around the droplet early during the coagulation step. Although the beads are porous, their porosity is poor because the immediate coagulation of the skin does not allow the skin to flow and thus the bead is very dense, with a small pore structure at and just below the skin.
U.S. Pat. No. 4,024,334 to Chandler et al is directed to cellulose acetate gel beads (gel beads are different from the foregoing microparticles which have no gel components). These gel beads are made by the steps of: (a) forming, at an elevated temperature, a dispersion of a solution of at least one cellulose ester in a liquid with which the solution is immiscible; (b) cooling the dispersion; and (c) then separating the beads from the liquid. This process causes the solvent to stay in the cellulose acetate bead and prevents precipitation and hardening, and thereby forms a gel bead.
U.S. Pat. Nos. 4,390,691 and 4,461,892, both to Nishikawa et al, are directed to cellulose particles made from a cellulose organic ester precursor. The process includes the steps of: (a) dissolving a cellulose organic ester in a chlorinated hydrocarbon solvent to form a solution; (b) adding the solution to an agitated aqueous medium and allowing the solvent is allow to evaporate; (c) regenerating the resulting cellulose organic beads that are still in the aqueous medium to cellulose; and (d) removing the cellulose particles from the aqueous medium.